Quantitative FISH analysis and in vitro suspension cultures of erythroid cells from maternal peripheral blood for the isolation of fetal cells

Culture of Cells from Maternal Circulation, in Conditions Favoring Fetal Endothelial Cell Expansion, Does Not Facilitate the Preferential Expansion of Circulating Fetal Cells

OBJECTIVES

To establish optimal culture conditions for fetal endothelial cells, and determine whether these can be used for preferential expansion of fetal cells from maternal blood.

METHODS

Human adult microvascular and umbilical vein endothelial cells were cultured in the presence of colony-stimulating factor-1 (CSF-1), placental growth factor (PlGF), and transforming growth factor-beta1 (TGF-beta1). The effect of each cytokine was assessed. We expanded peripheral blood mononuclear cells (PBMCs) from 18 pregnant women using the conditions most favorable to fetal cells; in specimens from women carrying male fetuses (n = 9), cell origin was determined by PCR (SRY locus).

RESULTS

The optimal concentrations of CSF-1, PlGF and TGF-beta1 were 10, 100, and 5 ng/ml, respectively. PBMCs from maternal blood expanded in the presence or absence of the cytokines; PCR analysis showed no Y sequences in cultured maternal samples.

CONCLUSION

Optimal concentrations of CSF-1, PlGF and TGF-beta1 for preferential expansion of fetal endothelial cells were determined in model cultures. However, when these conditions were applied to maternal blood samples, no fetal cells could be detected based on PCR for SRY in women carrying male fetuses.

Rare cell isolation using antibodies covalently linked to slides: application to fetal cells in maternal blood

We describe here a new type of method for isolation of rare cell populations in biological fluids. The method is based on the anthraquinone technology for covalent binding of molecules to a polymer surface. An anthraquinone molecule conjugated via a linker to an electrophilic group (AQ Immobilizer trade mark reagent, Exiqon A/S) is covalently bound to a polymer surface by UV irradiation. The electrophilic group of this AQ reagent can covalently bind a specific antibody directed against a specific cell marker. Applying a cell sample to the functional surface, the cells having the specific cell marker on the cell surface will bind to the antibody on the functional surface. Using this technique, even extremely small cell populations may be isolated. We succeeded in isolating fetal cells from maternal blood samples in the first trimester for chromosome defects genetic diagnosis.

Analysis of Fetal Blood Cells in the Maternal Circulation: Challenges, Ongoing Efforts, and Potential Solutions

The invasive procedures amniocentesis and chorionic villus sampling (CVS) are routinely applied in pregnancies at risk for fetal abnormalities and the results obtained are the gold standard for prenatal diagnosis. Because these methods of fetal cell procurement involve a 0.5-2% risk for fetal loss, they are recommended mainly in cases at high risk for fetal genetic or cytogenetic abnormalities. The development of a reproducible, reliable, noninvasive method based on retrieval of rare fetal cells from the maternal circulation will render testing feasible for the general population. Despite intensive investigation, a satisfactory, clinically acceptable method has not yet emerged. Several cell types have been targeted to this end, mostly nucleated red blood cells (NRBC), CD34+ hematopoietic progenitors, and trophoblasts. Although these cell types have been unequivocally proven to be present in the maternal circulation, each bears a significant disadvantage, rendering their application in clinical testing currently impossible: NRBC cannot be expanded in culture, thereby ruling out metaphase chromosome analysis, an essential component of prenatal diagnosis. CD34+ cells do posses the potential for in vitro proliferation, however, they have been found to persist in the maternal circulation after delivery, thereby complicating diagnosis in consecutive pregnancies. Trophoblasts are not consistently detected in the maternal circulation. Moreover, due to the lack of a definitive fetal cell marker and a reliable sorting method, foolproof fetal cell identification of any of these cell types is not possible. This report outlines the obstacles that impede development of a method for noninvasive fetal cell sampling for prenatal genetic diagnosis, along with a description of our efforts to analyze simultaneously two fetal blood cell types, NRBC and CD34+ cells in maternal blood during pregnancy, and the problems encountered. This work and that of others lead us to suggest potential future directions to help develop this important technique.

Non-invasive prenatal diagnosis: on the horizon?

The launch of the genomics and postgenomics era has greatly expanded our understanding of the genetic basis of many diseases. In conjunction with the sociocultural trend to delay childbirth and to maintain smaller family units, extra demand may be placed on the existing prenatal diagnostic services. The inherent risk of fetal loss associated with current prenatal diagnostic procedures, such as amniocentesis and chorionic villus sampling, has spurred research into non-invasive prenatal diagnosis. Much research has been conducted on the exploitation of fetal genetic material present in the maternal circulation. The initial focus was on the isolation of intact fetal cells and subsequently, the existence of extracellular fetal DNA in maternal plasma was realized. Exciting developments have been achieved in recent years. A large-scale trial to evaluate the clinical utility of fetal cell isolation from maternal blood for fetal aneuploidy diagnosis was launched and data were recently published. Much has taken place in the research of fetal DNA analysis in maternal plasma and in one example, namely prenatal RhD determination, this type of analysis has been used in the clinical setting. This paper reviews the technological developments in non-invasive prenatal diagnosis.

Fetal cells and DNA in maternal blood

Although fetal cells have been known to escape to the maternal circulation for a number of years, research attempts to use them for prenatal diagnosis have not had any consistent success. This review attempts to trace the history of such attempts and to document their progress and reasons for success or failure. The opinions of recent conferences including that of the US National Institute of Child Health and Human Development, a sponsor of major US research in the field, are reported and discussed. It is concluded that although basic work has demonstrated the biologic availability of both fetal cells and their free DNA representatives in the maternal circulation at gestational ages relevant to prenatal diagnosis, much work remains to develop practical technology for their consistent recovery and assay.

Comparison of methods for erythroblast selection: application to selecting fetal erythroblasts from maternal blood

BACKGROUND

Many methods have been employed to obtain fetal cells from maternal blood for prenatal diagnostics, but there has been little work done that compares the efficacy of different methods. This study presents a comparison of two commonly used methods for selecting erythroblasts with selection directly from whole blood.

METHODS

Erythroblasts were isolated from maternal blood by either differential lysis or density separation, followed by selection with an antibody to the transferrin receptor. These methods were compared with antibody selection directly from whole blood. The total yield of erythroblasts was determined for each method.

RESULTS

Red cell lysis is not recommended because the lysis step cannot be well controlled. Density separation followed by antibody selection works well. However, a faster and simpler method, antibody selection directly from whole blood using Immunicon Ferrofluid and magnetic separators, works as well and has the potential to yield even more cells.

CONCLUSIONS

Considering the need for a simple and quick method for selecting fetal cells from maternal blood, we suggest selection directly from whole blood.